Said insane clown being, of course, Donald Trump.
No one expects the debate to be an actual discussion of the issues. Trump will bluster, lie, insult, and boast. He will, in short, act like an asshole child. Biden will try to actually answer the questions posed to him. Those questions will be extremely biased in favor of Trump, given that the "moderator" will be---Jesus!---Fox News.
There's no valid reason for this stupid dog and pony show to ever take place. Neither candidate will "win," given the fact that no actual debating will occur. Foxy Wally will ask a question. Biden will answer it. Then Trump will ramble incoherently and nastily, paying no regard whatsoever to the actual question he was asked. (Or, those things will happen in reverse order if Trump goes first.) We'll have that over and over for 90 minutes.
Afterwards, I'm sure that Fox News, as well as our resident Trumper fools, will proclaim Trump the bigliest bestest winner of the debate EVER and crow that his performance will pave the way to a landslide victory in November by ELEVENTY SQUILLION ELECTORAL VOTES.
Conservitards are hoping that Biden will stammer or stutter or something and then they can place altered videos of it on Facebook over and over and over and over and over. One particularly Trumpy poster here will be completely unable to resist posting one or more of those images/videos. He is so obsessed with doing that, he still would if someone offered him $10,000 not to. Because Facebook is the ultimate source of TROOTY TROOT!
I doubt that the debate will benefit either candidate; Presidential debates have historically had little effect on actual election results. Hillary made the Orange Orangutan look like a fool three times, and the very base "base" didn't blink an eye. This time, Biden will look presidential, Trump will look like an ass, and it won't matter.